Method of soap-making



y 8, 1956 F. T. PALMQVIST 2,744,922

METHOD OF SOAP-MAKING Filed Dec. 6, 1952 4 Sheets-Sheet l IN V EN TOR.:redri/e 95x10) Pa lm gvisz y 8, 1956 F. T. PALMQVIST 2,744,922

METHOD OF SOAP-MAKING Filed Dec., 6, 1952 4 Sheets-Sheet 2 IN V EN TOR.yrm'ra'k Yador 2203px ICS y 1956 F. T. PALMQVIST 2,744,922

METHOD OF SOAP-MAKING Filed Dec. 6, 1952 4 Sheets-Sheet s ]N V EN TOR.fredri/e Yodor film grist $2M MW y 8, 1956 F. T. PALMQVIST 2,744,922

METHOD OF SOAP-MAKING Filed Dec. 6, 1952 4 Sheets-Sheet Soap by weighfNa Cl, 0 by weighf IN VEN TOR.

Un ted States Patent poration of Sweden Application December 6, 1952,Serial No. 324,585

4 Claims. (Cl. 260-418) This invention relates to an improved andsimplified process of soap-making. j

Heretofore soap has generally been produced according to the batch orboiler method in which fat and fatty oils are saponified with causticsoda in large caldrons. By thesaponification a homogeneous solution ofsoap in water is obtained from which the soap is subsequentlyprecipitated by adding. salt. This precipitation (the graining) resultsnot only. in .soap but also in a spent lye made up of water, glycerine,alkali, salts, and impurities. The soap is separated from the lye bygravity or centrifugal separation. From the spent lye, glycerine is thenobtained. The neat soap separated as described above is subjected to oneor more fitting operations in which water and some salt and lye solutionare added to the soap, whereupon the mixture .is brought to boil-' ing.This produces a mixture ofniger and neat soap. The latterisseparatedfrom the niger by gravity or .centrifugalseparation, whereuponthe neat soap is worked up to a marketable product.

The conventional method has several drawbacks. Thus, the totalmanufacturing time is at least eight days. During all this time the soapmass has a. temperature between 85 and 100 C., resulting in colordeterioration of the material. Further, the heat consumption is veryhigh because heat must be-is'u'pplied during the long processing time,amongother things to compensate the losses of heat which are unavoidablein spite of the insulation of the tanks. The, apparatus also requiresconsiderable space owing to'the large quantities of material beingsimultaneously processed. In other words, the capacity per unit of timeis low. From 'the point of view of the capital invested, it is also aconsiderable disadvantage that large-quantities of raw material are kepttied up in the manufacturing process for the considerable period of timementioned.

It is true that a few continuous soap making processes reducef'some ofthe above disadvantages, but the initial cost of the plants isoften'very high.

in the process of "the'present invention, which is applicableboth to theconventional method (the batch method) and the continuous method, thedisadvantages referred to have been eliminated; I

"According to the ,present invention, the grainingis ca'r'riedout withan aqueous solution of an electrolyte whichconsists wholly or in part ofalkali-hydroxide having jastrong grainingeifect. In this way, a mixtureis obtainedfrom-which theneat soap maybe easily. separated from thespentlye, for example, 'by gravity or centrifugal separation.

Owing to :the strong graining action of the electrolyte, a neatsoapphase with low electrolyte content is obtained, as will be explainedin more detail below. The electrolyte consisting substantially of alkalihydroxide must in some way be neutralized, as astrongly alkalinesoapl'i's'usuallynot desirable because thealkali irritates theskinu Inexperiments to neutralize the alkali. with fattyacid, difiiculties werealways encountered in that the soap thickened considerably, because itwas not possible to distribute the fatty acid evenly in the grainedsoap. Local portions of soap having a very high viscosity were formed,enclosing unsaponified fatty acid or acid soap. As a consequence, onbeing stored,'such soap showed discolorized local portions or rancidityspots.

The diificulty in the neutralizing has been solved, according to thecharacteristic feature of the invention, by neutralizing thealkali-hydroxide content with such an amount of bi-valent or poly-valentacids and/or acid alkali salts of such acids, for example, phosphoricacid, boric acid, silicic acid, carbonic acid, sulphuric acid, citricacid, oxalic acid, phthalic acid, etc., that the composition of the soapmass becomes such that the neat soap will be in phase equilibrium withniger, the neutralization being carried out with substantially noformation of free niger, that is, so that separation into neat-soap andniger is unnecessary. The acids form salts with .the excess alkali ofthe soap. The characteristic feature of the salts is their low grainingeffect.

The neutralizing agents referred to are usually added in the form ofwater solutions but may also, if required, be added in the form of afinely ground powder.

According to still another feature of the invention, the neutralizingmay'be'carried out with a water solution of one of the above. acidsand/or their acid alkali salts, in which solution fatty acids and/orsulphonic acids and/ or easily saponified fatand/ or colophony, etc.,have been emulsified. It has been proved in practice that, by takingthis step, the risk of forming a highly viscous soap is eliminated,because the electrolyte concentration around the soap formed becomesrelatively high.

The invention may behest explained with reference to a McBain diagramfor soap. Theaccompanying draw ings. show fivediagrams, .of which Fig. 1is a McBain diagram for soap; Fig. 2 is an enlargement of part of theFig. 1 diagram, illustrating examples of the practice of the invention;and Figs. 3, 4 and 5 are modifications of Fig. 2 illustrating otherexamples.

Referring to Fig. 1, the diagram there shown is for sodium soap of apure fatty acid, i. e., lauric acid, at C. On the diagram, thepercentage of electrolyte (by weight), in this case sodium chloride, ismarked on the abscissa, and the percentage of soap (also by weight) onthe ordinate. The reading of the composition at a point of the diagram,point a, for example, is made by following the right-angle co-ordinatesfrom the axes. Thus, the composition at point a is 2.0%

sodium chloride, 41.0% sodium laurate (soap), and the balance up tomakes 57.0% water. On the diagram, the neat soap zone is marked A, themiddle soap zone B, the niger zone C, the graining zone D, and thefitting zone E. The first three zones represent homogeneous phases,whereas the last two represent nonconcentration that the composition ofthe soap formed will lie within the area C, that is, in the niger zone(for.

example, point a). Sodium chloride or sodium chloride solution is thenadded to the niger, whereby the composition of the material passes overto the right into the. graining area, for example, point b of zone D. Asthis;

zone represents a non-homogeneous phase, the material can be dividedinto two pure phases by separating, that is, a neatsoap-phaserepresented by point of zone A, and a sp nt ye Phase of. very l w soapon a ut 0.3 to 0.5%, and of high electrolyte content, about 14% (point aof zone D). This spent lye keeps dissolved in it glycerine which hasbeen liberated from the fat during the saponification as. well as partof the impurities of the fat. The lye is passed to the glycerineextraction plant. The soap produced cannot yet be worked into amarketable product because it is not what is termed millable. Theconsistency is hard and the material is brittle, and the soap would notkeep together on being stamped.

In order to obtain a millable soap, the grained neat soap must beffi-tted, which means that its composition, .by adding water and a weakelectrolyte, is displaced downward obliquely to the left on the diagram,into zone E. This zone like the graining zone D represents anonhomogeneous phase, so. that the mass separates into two pure phases,one phase of fitted neat soap corresponding to a point on the boundaryline of the zone A, as well as a niger phase corresponding to a point onthe boundary line to zone C. Owing to the high viscosity and lowdifference in specific gravity between neat soap and niger, asatisfactory separation of the former from the latter takes about 3 to 4days. After the niger has been separated from the neat soap, the nigeris subjected to boiling in order to extract its soap content. Ifrequired, the niger may first be purified, as it now contains somefurther impurities from the neat soap. After drying and milling, thefitted neat soap may now be pressed into pieces of soap.

Zone A of the saponification diagram (Fig. 1) was above stated torepresent a homogeneous phase, the neat soap phase. As will have beenunderstood from the foregoing, however, the soap has different qualitieswithin this zone, depending upon what other zone it borders. Neat soapin phase-equilibrium with spent lye, that is, soap having a compositioncorresponding to a point on the boundary line of zone D, ischaracterized by high viscosity and cannot, as already'pointed out, bestamped into pieces of soap after milling. On the other hand, neat soapin phase-equilibrium with niger, that is, soap having a compositioncorresponding to a point on the boundary line of zone B, has asoft'consistency and can be easily worked. The explanation of this isthat the soap in zone A is made up of liquid crystals, the surfaces ofwhich are moistened by the mother lye from which they have beenprecipitated, that is, in the first case spent lye and in the secondcase niger. The spent lye with its low viscosity and high percentage ofsodium chloride is an inferior lubricant, which, among other things, canbe understood from the fact that it feels rough between ones fingers.This fact causes a great inner friction in the neat soap, that is, greatfriction between the soap crystals, and thematerial can flow only withdifliculty. The niger, on the other hand, is viscous, feels slippery andgives low inner friction to the neat soap. A neat soap inphase-equilibrium with niger is therefore soft and flows relativelyeasily.

The importance of the, mother lye with regard to the workability of thesoap has hitherto not been fully clear. The invention is largely basedon the facts stated above.

As will be seen from the diagram of Fig. 1, it is possible to move fromone zone of the diagram to another by adding various agents, forexample, water or electrolyte. Adding highly concentrated electrolytenormally results in a displacement to the right, though the effect ofthe various electrolytes in this respect is more or less pronounced.Thus, to obtain the same effect as with 1 part sodium chloride, it isnecessary to add, for example, 0.87 part sodium hydroxide, 1.30 partssodium acetate, 1.56 parts sodium nitrate, 1.84 parts sodium carbonate,2.00 parts sodium sulphate, 3.00 parts sodium tetraborate, 2.34 partstri-sodium phosphate, 2.34 parts sodium pyrophosphate, 2.8 to 3.7 partssodium silicate (depending on the NazOrSiO2 ratio) and about 6.7partspotassium silicate. It is said that the electrolytes have differentstrong graining actions because larger quantities are required of someof them than of others in order to transfer the niger phase (zone C) tothe graining zone D. It will also be understood from the above that whenan electrolyte with strong graining effect is used, the electrolytepercentage will below in the neat soap phase and the spent lye, whereasit will be high in both phases when an electrolyte with mild grainingaction is used. As will. l be, seen from. th above figures, soda lye hathe strongest grainingefieot of the electrolytes mentioned.

On the other hand, by the addition of a further electrolyte in the formof a water'solution of bi-valent or polyvalent acid (or acid alkalisalts thereof) to an alkalihydroxide-containing neat soap, in theneutralization according to the present invention, the displacementoccurs to the left instead of to the right in the diagram. In otherwords, the displacement will be into the fitting zone, if the startingmaterial was. a neat soap in phaseequilibrium with spent lye. Thus, totake an example, 1 mole phosphoric acid binds 3 moles sodium hydroxidewith the graining coefiicient 0.87 to a single mole trisodium phosphatewith the graining coefiicien-t 2.34. The neutralizing may be conductedso that the amount of niger formed becomes so small that separation intoneatsoap and niger is not necessary, the form of the soapmass at thisstage allowing it to be directly worked in the usual way to amarketable, product. The fitting stage is thus seemingly omitted, butnevertheless a soap is obtained with the characteristic malleabletexture produced by the fitting process and necessary to get aready-to-use soap. of good quality;

The invention has been explained above with reference to a neat soapwhich has been grained out mainly with alkali hydroxide, and thentransferred to a millable stage by wholly or partly neutralizing thealkali hydroxide with poly-valent acids or acid salts. thereof, themother lye between the soap crystals also being transferred in this wayfrom spent lye to niger The soap produced has thereby become millable.However, it may be pointed out that grained neat soap must also includesoap which has aldready been subjected to the usual fitting but owing tosubsequent temperature changes, or the like circumstances, has againassumed the character of a grained neat soap. (The McBain diagram has,consequently, a different appearance at different temperatures.) Such asoap can also to advantage be treated according to the presentinvention, provided that it has a certain remaining alkalinity.

The invention Will now be explained in more detail with reference to thefollowing examples, inwhichall statements concerning parts andpercentages refer to weight. 1

Example 1 This example refers toa case inwhich neat-soap, made up ofsodium laurate and. grained. mainly with. alkali hydroxide, istransferred into a millable and stampable state by phosphoric acid.

639 parts of lauric acid triglyceride are saponifiedwith 991 parts of15% soda lye (the equivalentof 148.5 parts dry sodium hydroxide). This,produces a niger holding 667 parts of soap (dry weight), that is, thesoap per.- en a of the. R se s 4-1%- The nicerv also. containsfreesodium hydroxide in an amount of 1.75 %,v which,,with re gard tograiningefiect, corresponds to 2% sodium chloride. The composition ofthe nigerthus answers to Point a of the diagram, Fig. 1.

e. n ce s. st ned with. 17 par s of 35%. oda y (6,1.6 parts dry NaQH)and parts of 20% sodium horide soluti n (2 par s. aCl.)-

he rai ims; agent d the sodiutnhy roxide. conten of, he niger givesaNaQH=NaCl atio. correspondingto 4.5: 1. Byadding the graining agent, a.displacement takes place on the diagram of Fig. 1 from point afto pointb(35.0%. soap and 6.5% electrolyte, calculated as NaCl),

which latter point is situated within the graining zone D near itsboundary with the nigerzone C.

When separating the grained soap from the lye (by gravity or centrifugalseparation) a neat soap is obtained which contains 57.2% soap and 1.9%electrolyte, calculated as NaCl. The neat soap corresponds to pointc ofthe diagram. The spent lye obtained by the separating has a compositioncorresponding to d of the diagram (0.5% soap and 13.7% electrolyte,calculated as NaCl).

The above neat soap'has 'a content of free sodiumhydroxide. of 1.38%.According to the present invention, part of the free alkali isneutralized with 30% phosphoric acid. When adding 1.04 parts ofphosphoric acidto 100 parts of neat soap a displacement'takes place frompoint c of Fig. 2 (identical with point c of Fig. 1, Fig. 2 being anenlargement ,of part ofthe diagram of Fig. 1) to point e, in which theNaOH percentage has dropped to 0.99%, by the addition of phosphoricacid. The point e, which is also located within the neat soap zone A,corresponds to 56.6% soapand 1.67% NaCl. By adding another 1.86 parts ofphosphoric acid the content of free alkali of the neatsoapis lowered to0.31%, or: to point 7 which is situatediin the fitting zone E. Thispoint cor responds to 55.6% soap'and 1.28% NaCl.

Example 2 Starting from point c of Fig. 2, the free alkali of the neatsoap is wholly neutralized with 50% NaH2PO4 (4.14 parts solution to 100parts soap). A displacement then takes place to point g within thefitting zone E. Point g corresponds to 54.9% soap and 1.46% electrolyte,calculated as NaCl. 7 I,

Example 3 This example shows how toilet soap grained out mainly withalkali hydroxide is made stampable by neutralizing with mono-sodiumphosphate. The fat used in the manufacture wasa mixture of tallow,bone-fat, palm oil, and cocoanut fat. By graining out the niger mainlywith alkali hydroxide a neat soap was obtained, thecomposition of whichanswers to point h of the diagram-of Fig. 3, or 71.2% soap and 0.52%electrolyte calculated as NaCl. The electrolyte is actually made up of0.09% NaCl and 0.37% NaOH. On adding l.l parts of 30% NaH'zPO4 to 100parts of neat soap, the NaOH percentage is reduced to 0.15%, and thecomposition of the material passes to point i of the fitting zone B,which corresponds to 70.4% soap and 0.45% electrolyte calculated asNaCl.

Example 4 By adding another 0.75 part of 30% NaHzPOr solution to thesoap of Example 3, all free NaOH is neutralized and the compositionpasses to the point jv which is also situated within the fitting zone E.The point i corresponds to a composition of 69.9% soap and 0.41%electrolyte calculated as NaCl.

Example 5 This example uses as starting material soap according toExample 3 which is neutralized with an emulsion of oleic acid in a 30%NaH2PO4 solution. The ratio beaccording to the same example, a' soap isproduced having a composition which corresponds to point I of thediagram (Fig; 3), that is, with 70.35% soap and 0.35% electrolytecalculated as NaCl. All sodium hydroxide has been neutralized.

Example 7 v p This example refers to a case in which toilet soap madefrom the identical fat mixture mentioned in Example 4, is grained andthen fitted mainly with alkali hydroxide,

, in order to obtain a quicker gravity separation or a higher throughputin a continuously operating plant, whereupon the alkaline neat soap isneutralized with an emulsion of oleic acidin mono-sodiumphosphatesolution according to Example 5, to render harmless the alkali of thesoap. Referring to Fig. 4, the product obtained is neat soap of acomposition corresponding to point m of the diagram,

that is, 70.9% soap and 0.48% electrolyte calculated as NaCl. Theelectrolyte is actually made up of 0.33% NaOH and 0.10% NaCl. 1.25 partsof an emulsion containing 0.33 parts oleic acid and 0.92 part of 30%NaHzPoi solution are added'to 100 parts of this neat soap. In this way,a soap is produced having a composition which corresponds to point It inthe diagram,.that is, 70.4% soap and 0.37% electrolyte calculated asNaCl. The sodium hydroxide percentage has been lowered to 0.10%. 1

By means of the above process, marketable productscan be obtained in aconsiderably reduced manufacturing time when using the batch method, orwith a larger throughput rate of the plant when using continuousmanufacturing methods. The time-consuming fitting-operation may thus beavoided and one or more grainings mainly with alkali hydroxide may besubstituted, depending upon how bright the color of the soap should beand to what degree it is desirable to recover the glycerine. When only.

one alkaline graining is made, the time of production is reduced fromabout 6 days to 2 days.

In continuous soap making in which centrifugal separators are used, forexample, the manufacturing process is considerably simplified and thecapacity of the plant increased when the present method is utilized.Thus, a bright soap may be made by two alkaline grainings, which meansthat the throughput rate of the separators can be increased to twice therate when working according to the old method with normal graining andfitting- By using mainly alkali hydroxide for graining, a considerablybrighter soapisobtained than when an electrolyte of conventionalcomposition is used.

v tralization according to the present invention, further adtween oleicacid and mono-sodium phosphate in the emulsion is 20:80, with regard tothe neutralizing action of the oleic acid and the phosphate on the freeNaOH con- Example 6 By adding another 0.81 part of the emulsionspecified in Example 5 to the partially neutralized soap obtainedvantages may be gained. Thus, alkali phosphates, for

example,.improve the qualities of the soap in that, when i using hardwater, an extra consumption of soap is avoided because the lime saltsdissolved in the water react with the phosphates and form calciumphosphates and not with alkali salts of fatty acids. That is, theformation of lime soap is avoided. Depending upon what phosphoric acidsalts are used, all precipitation of lime may also be prevented byusing, for example, tripolyphosphate or a polymetaphosphate. These saltsare capable of forming watersoluble complex salts with those substanceswhich render the water hard. When the'neutralizing is made, for example,with phosphoric acid in combination with a polymeric alkali phosphate orwith acid alkali salts of some polyphosphoric acid (for example, acidtripolyphosphate), a still better efiect than with orthophosphate isobtained, because at the same time that the soap mass is neutralizedExample 8 The alkali content of soap according to Example 3 is partlyneutralized with CO which with water in the soap forms H2603, which is abi-valent acid. To 100 parts of neat soap with a composition accordingto point 11 in the diagram of Fig. 5 :are added 1.3 parts of water andfurthermore 0.12 parts of CO2 by allowing carbon dioxide gas to bubbleinto the soap mass. In this way the Composition of the neat soap isdisplaced to point of Fig. 5. Said point answers to the followingcomposition: 702%. soap and 0.34% electrolyte, calculated as NaCl. Afterthe treatment the NaOH content amounts to 0.15%.

Example 9 The sodium hydroxide content of soap according to Example 3 iscompletely neutralized with an emulsion of lauric acid in 12.5% NaHzPOtsolution. The ratio between the lauric acid and the mono-sodiumphosphate is 50:50 as regards the neutralizing eifect of the respectivecomponents on the content of free NaOH of the soap. To 100 parts of neatsoap with a composition according to point h of Fig. are added 3.15parts of an emulsion consisting of 0.925 parts of lauric acid and. 2.225parts of mono-sodium phosphate solution. The composition of the neatsoap is in this way displaced to the point p of Fig. 5. The compositionin this point is 70.0% soap and 0.32% electrolyte, calculated as NaCl.

Example 10 100 parts of neat soap with a composition according to pointhof Fig. 5 are added 1.04 parts of an emulsion consisting of 0.135 partsof rosin, 0.09 parts of. cocoa nut fat and 0.815 parts of mono-sodiumphosphate solution. After this addition the soap has a compositioncorresponding to point r of the diagram. The composition in this pointis 70.7% soap, 0.44% electrolyte, calculated as NaCL'and 0.20% NaOI-I.

Example 11 Soap according to Example 3 is neutralized with an emulsionof dodecylbenzenesulphonic acid in 15% NaHSOs solution, so as to reach afinal alkalinity of 0.15

NaOH. The ratiobetween the dodecylbenzenesulphon'i'e acid and themonosodiumsulphate "is :40, as regards the neutralizing effect of therespective components on the content of free NaOH of the soap. To partsneat soap with a composition according to point h of Fig. 5 are added2.84 parts of an emulsion consisting of 1.08 parts ofdodecylbenzenesulphonic acid and 1.76 parts of 15% NaHSO4 solution. Thecomposition of the neat soap 'is in this Way displaced to the point s ofFig. 5. The composition in this point is 70.35% soap, 0.41% electrolyte,calculated as NaC-l, and 0.15% NaOH.

In the examples described above there are no statements aboutemulsifying and stabilizing agents for the emulsions used asneutralizing agents. To those skilled in the art it -is obvious thatsuch agents are advantageously used. As an emulsifying agent there canbe added a minor quantity (about 0.1 to 2%) of a compound acting in anacid medium, such as sodium-dodecylbenzenesulphonate ordodecylbenzenesulphonic acid. If the latter is used, its neutralizingeffectmust be taken into consideration. The emulsion can be stabilizedby means of a colloid, which can be effected for instance by bringingthe silicic acid of Water-glass with a high SiOz content to precipitate.

I claim:

1. In the art of soap-making wherein soap is grained out with an aqueoussolution of an electrolyte made up at leastpartly of alkali hydroxide,and is then separated as neat soap from the spent lye, the improvementwhich comprises neutralizing the alkali hydroxide content of the neatsoap with an agent selected from the group consisting of bi-valent andpoly-valent acids and the acid alkali salts thereof, said neutralizingagent being added in a quantity such as to produce a soap mass in whichthe neat soap is in phase equilibrium with niger, said neutralizingbeing carried out with substantially no formation of free niger.

2. The improvement according to claim 1, wherein the neutralizing iscarried out with a water'solution of said agent in which a substanceselected from the group consisting of fatty acids, sulphonic acids,readily saponified fat and colophonyhas been emulsified.

3. The improvement according to claim 1, wherein said agent is one whichforms a salt having a low graining eiiect.

4. The improvement according to claim 1, wherein said agent is oneforming surface-active compounds with the alkali hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS284,313

1. IN THE ART OF SOAP-MAKING WHEREIN SOAP IS GRAINED OUT WITH AN AQUEOUSSOLUTION OF AN ELECTROLYTE MADE UP OF AT LEAST PARTLY OF ALKALIHYDROXIDE, AND IS THEN SEPARATED AS NEAT SOAP FROM THE SPENT LYE, THEIMPROVEMENT WHICH COMPRISES NEUTRALIZING THE ALKALI HYDROXIDE CONTENT OFTHE NEAT SOAP WITH AN AGENT SELECTED FROM THE GROUP CONSISTING OFBI-VALENT AND POLY-VALENT ACIDS AND THE ACID ALKALI SALTS THEREOF, SAIDNEUTRALIZING AGENT BEING ADDED IN A QUANTITY SUCH AS TO PRODUCE A SOAPMASS IN WHICH THE NEAT SOAP IS IN PHASE EQUILIBRIUM WITH NIGER, SAIDNEUTRALIZING BEING CARRIED OUT WITH SUBSTANTIALLY NO FORMATION OF FREENIGER.